Measuring the rate of flow of material in a conduit is an essential activity in many an industrial process. The invention disclosed herein is a result of work in world of metal castings. In that world companies cast parts using molten Magnesium, Aluminum, other metals, and alloys of metals. The companies have long sought a reliable flow meter so that they knew how much material and at what rate they were filling a mold. The axiom is true that if one cannot measure something, then he cannot manage it. The measurement allows someone to close the quality control loop, for instance, by experimenting with different fill rates and seeing which results in a better casting. Such management is impossible unless the manager can measure the rate of flow of material in a system.
In the case of molten metals that are highly corrosive or at high temperature, there has been no good flow meter. Previously, persons interested in measuring the flow of a molten metal in a pipe would have used either a linear annular induction flow meter or an electromagnetic flow meter where the electrodes needed to be in contact with the moving material. Such electrodes would need to be insulated from the conduit or pipe which presented problems for material selection and manufacturability while the electrodes themselves needed to be able to withstand and survive long-term contact with the flowing material. What has been needed is a flow meter that did not require physical contact between the measuring device and the material being measured. The present invention addresses those needs.
There are other flow meters. Some flow meters use an impeller and count the speed or revolutions of the impeller but such a system would not function where a metal melted or fouled the impeller. There are also sonar based systems but such systems will not work on materials that would corrode transducers. There are Doppler flow meters but such meters will not work unless there are impurities present in the flow.
An electromagnetic flow meter operates on the premise of Faraday's Law. For an electromagnetic flow meter one needs a conductive fluid and something that emits magnetic force. The magnetic force compels charged particles in the flow to separate into positively-charged particles and negatively-charged particles. The flowing of conductive fluid in a conduit through a magnetic field will induce a current of electricity. The induced voltage ε generated in the magnetic field B due to a conductive liquid moving at velocity v is thus given by:ε=Blv.where l is the distance between electrodes in the magnetic flow meter.
In a typical electromagnetic flow meter, a conduit is fitted with field coils on either side of a measuring tube. Two electrodes are fitted in the tube at right angles to the field coils. A non-polar insulating sleeve is often fitted in the tube to avoid the communication of charge to the metallic tube in which the fluid is conveyed. The field coils apply a magnetic force across the measuring tube perpendicular to the direction of flow. At rest, the positively-charged and negatively-charged particles in the conductive fluid are evenly distributed throughout the fluid. When the fluid starts to move through the measuring tube, then positively-charged and negatively-charged particles are separated out and tend toward one of the electrodes. An electrical voltage forms which is detected and measured by the two electrodes. That voltage is directly proportional to the velocity, and, together with the known measuring tube diameter, the rate of flow can be calculated. In order to eliminate interference voltage, the polarity of the field coils alternate at regular intervals. In some instances the data collected is otherwise treated to remover noise in the signal. There are many problems with the traditional electromagnetic flow meter including the cost of field coils, equipment to alternate the coils, exciters sometimes employed, equipment used to cleanse the “noise” from data collected. There is also the reliability problem associated with the increase in probability that something will break because of pieces employed. One can find aspects of this approach to flow measurement in numbers of patents issued.
The inventor is aware of the following patents and publications in the flow meter arts:
1. U.S. Pat. Nos. 6,505,517, 7,343,817, 6,505,517, 5,544,532, 6,611,770, 7,503,227, 5,578,763, 5,551,306, 6,865,956, 7,421,908, 7,509,852, 7,654,318, 7,124,645, and,
2. Patent Publications 2002/0189337, 2008/0296208, 2005/0109120, 2002/0190444.